The cornea is a transparent avascular tissue with a diameter of about 1 cm, covering the front surface of an eye ball. The conjunctiva is a mucous membrane covering the back surface of the eye lid and the surface of an eye ball which is posterior to the corneal limbus. The cornea and the conjunctiva serve an important role in vision. It is known that visual function is seriously affected when a disorder occurs therein. Keratoconjunctive disorders induced by various diseases such as corneal ulcer, keratitis, and dry eye are disorders caused by a delay in recovery from a disorder due to some reason such as an external injury or by a disorder that has become chronic. Since the cornea is a tissue that is connected to the conjunctiva, such diseases negatively affect each other in the normal construction of the epithelium and in some cases harm the structure or functioning of the corneal stroma or endothelium.
Collagen (especially type I collagen) is known as one of the representative stromal components of corneal parenchymal tissue. A functional disorder resulting from stromal degradation occurs in diseases due to a keratoconjunctive disorder. Thus, suppression of degradation of collagen (especially type I collagen) is considered effective against diseases caused by a keratoconjunctive disorder.
In a keratoconjunctive disorder, scar tissue, which is often formed after an inflammation has calmed, may obstruct the visual function. For this reason, suppression of collagen contraction, if possible, is considered effective against contraction and formation of scars (hereinafter, referred together as “scar formation”) as in the above-described suppression of collagen degradation.
Patent Literature 1 describes that all-trans retinoic acid (hereinafter, also referred to as ATRA) promotes corneal regeneration. However, the effect thereof is weak and the detailed mechanism thereof is yet to be elucidated.
Further, ATRA is an agonist of retinoic acid receptors (hereinafter, also referred to as RAR). However, since ATRA does not have selectivity with respect to RAR subtypes RARα, RARβ, and RARγ, the contribution of each RAR subtype to corneal regeneration effects is unknown.
Meanwhile, RAR is involved in various effects such as growth, morphogenesis and differentiation in many cells, such as inflammatory cells, immune cells, and structural cells. Further, it is verified that there is a difference in the distribution of RAR subtypes depending on the tissue or organ of a mammal.
Some of the effects of RAR are undesirable, such as increase in triglyceride due to RARα. Thus, the specificity or selectivity with respect to subtypes in compounds with RAR agonist activity is expected to lead to reduction in risk of side effects.
For the above reasons, there is a demand for RAR agonists, which have a strong effect of suppressing keratoconjunctive disorders and are highly safe based on subtype selectivity.
Patent Literatures 2 and 3 disclose the RAR agonist (E)-4-(2-{3-[(1H-pyrazole-1-yl)methyl]-5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-2-yl}vin yl)benzoic acid and the derivatives thereof. Further, Patent Literature 2 describes that (E)-4-(2-{3-[(1H-pyrazole-1-yl)methyl]-5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-2-yl}vin yl)benzoic acid is useful against pulmonary emphysema, cancer, and dermatosis. Patent Literature 3 describes that the above-described agonist is useful against neurological pain.
In addition, Non-Patent Literature 1 describes that the RAR agonist 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene acid induces apoptosis in lung cancer cells.
Furthermore, Patent Literature 4 describes that the RAR agonist 3-fluoro-4-[2-hydroxy-2-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-2-yl)acetylamino]benzoic acid is useful in muscle repair or regeneration.
However, pharmacological effects on keratoconjunctive disorders or scar formation resulting from keratoconjunctive disorders are not discussed or reported for any of the RAR agonists. In addition, there is no literature that suggests such an effect.